The invention relates to a method of physical channel power control in a radio system, the method comprising: establishing a physical channel with at least one spreading code; placing at least one service in the physical channel; performing physical channel power control according to the carrier/interference target set for the physical channel.
According to the prior art power control is performed on a physical channel on the basis of one carrier/interference target defined for it. In the prior art only one kind of service has been transferred on the physical channel at a time. If several different services are transferred simultaneously on the physical channel, e.g. user""s speech, moving video images or data, problems arise because power control is not optimized as the channel conditions change. Each service has quality requirements of its own and different channel coding and interleaving solutions. At the beginning of establishment of a radio connection it is difficult to predict which would be a suitable carrier/interference target of power control and how the physical channel should be divided between different services. During the connection transmission power is controlled on the basis of the service which requires the highest transmission power on the physical channel in question. This wastes radio capacity of the system because use of a high transmission power causes interference to other physical radio channels.
When the services use discontinuous transmission, the carrier/interference target of fast power control is maintained the same even though all services would not continuously use the resources of the physical channel. When only one carrier/interference target is defined for a physical channel, controlling of it is a very slow process. The reason for this is that in this case the target is based on a service requiring a very low error ratio, and thus defective frames are relatively infrequent at the receiving end.
In the existing IS-95 system it is not known to transfer parallel services on one physical channel. In the broadband version of the IS-95 system, W-cdmaOne, the problem is solved by using parallel physical channels. Services that require a high transmission rate are transferred on separate additional channels, and a carrier/interference target is defined separately for each of them. The disadvantage of this solution is that power control has to be performed separately on each additional channel, which increases the signalling load.
In conclusion it can be stated that the problem has not occurred earlier, or separate physical channels have been used for solving it, in which case the power of each physical channel can be controlled separately.
An object of the invention is to provide a method and an apparatus implementing the method in order to solve the above-mentioned problems. This is achieved with a method described in the preamble, which is characterized by: selecting one service from among the active services placed in the physical channel using a predetermined selection method; setting the carrier/interference target of the one selected service to lead the physical channel power control.
The invention also relates to a radio system comprising: a spreader for establishing a physical channel with at least one spreading code; a multiplexer for placing at least one service in the physical channel; a control arrangement for performing physical channel power control according to a carrier/interference target set for the physical channel.
According to the invention the radio system is characterized in that: the control system selects one service from among the active services placed in the physical channel using a predetermined selection method; the control arrangement sets the carrier/interference target of the one service selected from among the active services to lead the physical channel power control.
Preferred embodiments of the invention are disclosed in independent claims.
The invention is based on the idea that not only one carrier/interference target is rigidly set for the physical channel, but a separate carrier/interference target is set for each service. The service requiring the highest carrier/interference target is selected from among active services, i.e. services causing traffic on the radio path at a given moment, and the carrier/interference target of this service is set to lead power control of the whole physical channel. The method is dynamic, i.e. the carrier/interference target of the physical channel changes according to the services that are activated or inactivated.
The method and system of the invention provide several advantages. Since power control is based on the services transmitted at a given moment and the requirements set by them, power control corresponds to the reality better. In particular, use of too high a transmission power can be avoided, which decreases interference on the radio path and thus increases the amount of radio capacity available in the system. The need for signalling does not increase since power control is performed on one physical channel.